Ultra-QuickSort(归并排序求逆序对数)

Time Limit: 7000MS		Memory Limit: 65536K
Total Submissions: 34283		Accepted: 12295

Description

In this problem, you have to analyze a particular sorting algorithm. The algorithm processes a sequence of n distinct integers by swapping two adjacent sequence elements until the sequence is sorted in ascending order. For the input sequence 
9 1 0 5 4 ,
Ultra-QuickSort produces the output 
0 1 4 5 9 .
Your task is to determine how many swap operations Ultra-QuickSort needs to perform in order to sort a given input sequence.

Input

The input contains several test cases. Every test case begins with a line that contains a single integer n < 500,000 -- the length of the input sequence. Each of the the following n lines contains a single integer 0 ≤ a[i] ≤ 999,999,999, the i-th input sequence element. Input is terminated by a sequence of length n = 0. This sequence must not be processed.

Output

For every input sequence, your program prints a single line containing an integer number op, the minimum number of swap operations necessary to sort the given input sequence.

Sample Input

5
9
1
0
5
4
3
1
2
3
0

Sample Output

6
0

//归并排序模板，只加了一句 cnt += m-p;

#include<stdio.h>
#include<string.h>
long long  cnt;
int num[500010],tmp[500010];
void merge_sort(int num[],int x, int y, int tmp[])
{
    if(y-x > 1)
    {
        int m = x + (y-x)/2;
        int p = x, q = m, i = x;
        merge_sort(num,x,m,tmp);
        merge_sort(num,m,y,tmp);
        while(p < m || q < y)
        {
            if(q >= y || (p < m && num[p] <= num[q]))
                tmp[i++] = num[p++];
            else
            {
                tmp[i++] = num[q++];
                cnt += m-p;
            }
        }
        for(i = x; i < y; i++)
            num[i] = tmp[i];
    }
}
int main()
{
    int n;
    while(~scanf("%d",&n) && n)
    {
        for(int i = 0; i < n; i++)
            scanf("%d",&num[i]);
        cnt = 0;
        merge_sort(num,0,n,tmp);
        printf("%I64d
",cnt);
    }
    return 0;
}